Impressions - October/November 2020 - 42

Any dryer
used for curing
plastisol ink
needs to be
capable of
reaching
temperatures
above 320˚F,
with a conveyor
that can keep up
with production
flow.
thickness of a cake. Both require the same
oven temperature, but the cake requires a
longer oven dwell time.
Water-based inks are manufactured with
different "ingredients," but also contain
some form of plasticizer and resin. The
main difference between plastisol and
water-based inks is that certain water-based
inks can be cured by air drying. However,
most modern water-based inks need heat
in order to fully cure.

A donut probe is a small, 3-inch
plastic ring with small crisscrossed
wires in the center.

The donut probe is connected to a thin,
10- or 12-foot cable, allowing it to run
through the dryer and read the temperature
in real time.

Dryer Types
Dryers are essential in screen printing and
can determine a shop's product quality.
If shirts don't get cured properly, ink can
scratch or wash off the garment.
What should you look for in a dryer?
Essentially, any dryer used for curing plastisol ink needs to be capable of reaching
temperatures above 320˚F, with a conveyor
that can keep up with production flow.
The two types of dryers available on the
market are gas and electric models. The
former generates heat using actual flames
to reach the desired temperature inside the
dryer.The hot air then is blown across the
conveyor belt, creating an even heat level
throughout the chamber. To save energy,
some of this hot air is recycled through the
heat chamber, creating a convection heat
effect similar to a convection oven used in
kitchens.This makes gas dryers more efficient to operate, but also more expensive
to manufacture.
Heat generated from a flame is very dry
and can cure water-based inks, including
P.42

discharge inks, very well. It's possibly the
most preferred way to cure plastisol, but also
is the ideal dryer type for water-based inks,
which must have the water removed from
the ink film before the chemistry crosslinks the molecules, making the film solid.
Electric dryers typically use infrared (IR)
heating elements that are installed throughout the heat chamber directly above the
conveyor belt.They tend to be less expensive
than gas dryers and are available in smaller
sizes.
However, the lower-cost models can
have hot spots where heat is concentrated
unevenly in the chamber, causing the fabric
or ink to scorch if not properly handled.

I M P R E S S I O N S M A G . C O M OCT./NOV. 2020

Some higher-quality electric heaters have
internal fans that blow the air inside the
chamber, thus creating more even temperature throughout.
Controlling Dryer Temperatures
Due to its convection effect, controlling the
temperature in a gas dryer can be done more
accurately than in an electric dryer. One of
the reasons for this is that infrared energy
heats objects, not air.These objects, depending on what they are and how they absorb
the energy, can be heated at different rates.
For example, color can determine the
absorption rate, as dark colors absorb heat
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